This invention relates to a variable displacement vane pump.
U.S. Pat. No. 7,070,399 (corresponding to Japanese Patent Application Publication No. 2003-172272) shows an oil pump arranged to vary an outlet amount by a swing motion of a cam ring, and thereby to improve energy conservation. Moreover, in this oil pump, a hydraulic pressure in a vane back pressure groove of an inlet region is decreased to decrease a driving resistance of the pump, and thereby to further improve the energy conservation.